1. Field of the Invention
The present invention relates to a magnetic levitation type vacuum pump and a magnetic levitation device.
2. Description of Related Art
In a turbo molecular pump in which the rotor is magnetically levitated by using a superimposed sensorless magnetic levitation device, a carrier wave of higher frequency whose frequency band is subject to a magnetically levitation control is superimposed to a driving current of the electromagnet for magnetic levitation so that the distance between the electromagnet and the rotor is measured from the voltage value, the current value and so on of said carrier wave (e.g., Japan Patent Publication No. 1994-313426).
When the coil turns are reduced in order to improve the coil characteristics (e.g., loss due to inductance, distributed capacitance regarding to inductance) regarding (e.g., loss due to inductance, distributed capacitance regarding to inductance) regarding to the carrier wave as well as in order to increase the carrier wave current, it may lead to a problem that the magnetic levitation control is affected since the desired magnetic levitation force cannot be obtained, etc. In such condition, in order to obtain the desired magnetic levitation force, it is necessary to increase the electromagnet current; thus the increase of power necessary for the magnetic levitation is resulted. Since a plurality of vacuum pumps are disposed in a semiconductor manufacturing device, the increase of power of vacuum pumps leads to an increase in power of the entire semiconductor manufacturing device and it is not preferred from the viewpoint of energy conservation.
On the other hand, in the case that the supported body is levitated by a small electromagnet current, it is necessary to increase the coil turns of the electromagnet. However, if the coil turns of the electromagnet is increased, the carrier wave current component (the current component corresponding to the carrier wave signal) is decreased and the position measurement of the supported body which uses the carrier wave becomes harder. In addition, the deterioration of the coil characteristics at high frequencies cannot be neglected.